The colon (:) is used in several ways.
Here are some of them:
a. to show that there is a list of things or a quote following.
Future action includes: strengthening public health engagement around trade and health issues; further research and more effective communication of research to public health advocates, trade policy officials and stakeholders from other sectors; and a stronger intersectoral collaboration between public health advocates, trade experts and advocates from other sectors. (Gleeson and Legge, 2012)
b. to separate two clauses where the second gives details or examples of the first.
I remember Mr Hubble as a tough, high-shouldered, stooping old man, of a sawdusty fragrance, with his legs extraordinarily wide apart: so that in my short days I always saw some miles of open country between them when I met him coming up the lane. (from Charles Dickens’ Great Expectations)
c. to show a ratio or proportion.
That horse has 1:3 odds of winning.
d. with time.
It’s now 5:03 am.
e. to refer to chapters and verses in the Bible.
John 3:16 is the most well-known verse in the Bible.